1. Field of the Invention
The present invention relates to a structure of a biometric identification device and, more particularly, to a biometric identification device having sensing electrodes with multiple connection selections.
2. Description of Related Art
Biological feature sensing and comparing technologies have been maturely and widely applied in identifying and verifying the identity of a person. Typical biometric identification types include fingerprint, voiceprint, iris, retina identification, and the like. For consideration of safe, comfortable, and efficient identification, the fingerprint identification has become the most popular one. The fingerprint identification generally requires a scanning to input a fingerprint or a finger image of a user and store the unique features of the finger image and/or the fingerprint for being further compared with the fingerprint reference built in a database so as to identify or verify the identity of a person.
The image input types of the fingerprint identification include optical scanning, thermal image sensing, capacitive sensing, and the like. The optical scanning type is difficult to be applied in mobile electronic devices due to its large volume, and the thermal image sensing type is not popular due to its poor accuracy and reliability. Thus, the capacitive sensing type gradually becomes the most important biometric identification technology for the mobile electronic device.
In prior capacitive image sensing technology, the sensing electrodes and the detecting circuit are typically implemented on a single integrated circuit (IC) to increase the signal to noise ratio (SNR) and signal detection quality. The capacitive image sensing can be divided into two types, including a linear swiping scan and a full area detection. The positioning recovery of the former one is difficult, which may cause the image distortion and poor image quality. The latter one requires an IC manufacturing process to make sensing electrodes, which results in a large wafer area to be used and a relatively high cost. In addition, both of them have the drawbacks of complication and difficulty in packaging, poor mechanical strength, fragility, susceptible to moisture erosion damage, and the like, and thus the reliability and the usage lifetime of the device are not users satisfied.
FIG. 1 is a schematic diagram of a typical capacitive sensing. As shown in FIG. 1, there is a substrate 110 implemented thereon a plurality of sensing electrodes 120. Each sensing electrode 120 is electrically connected to a controller 140 via a corresponding trace 130. When the finger of a user comes into touch with the substrate 110, the controller 140 respectively drives the sensing electrodes 120 to perform a self-capacitance sensing. For obtaining a sensed image of the fingerprint, the controller 140 requires reading sensed signals on the sensing electrodes, respectively. When the controller 14 reads the sensed signal of the sensing electrode 121 from the trace 131, the sensed signal of the sensing electrode 121 is likely to be affected by the sensed signals on the surrounding sensing electrodes 122, 123, as well as the sensed signals on the traces 132, 135. Such a phenomenon becomes more obvious when the size of the sensing electrode 120 is reduced. As a result, the sensing resolution of the fingerprint identification device cannot be increased.
Therefore, it is desirable to provide an improved biometric identification device to mitigate and/or obviate the aforementioned problems.